1. Field of the Invention
The present invention relates, in general, to a broadcasting antenna for a vehicle and a shark fin antenna apparatus having the same, and more particularly to a broadcasting antenna for a vehicle and a shark fin antenna apparatus having the same, which includes a helical radiation unit made up of a plurality of helical radiators and having a coupling feed structure and an extended radiation unit made up of a plurality of top loaders, each of which includes a band stop filtering unit and conductive patterns, thereby improving radiation efficiency and preventing signal interference.
2. Description of the Related Art
With the development of wireless communication technology, a variety of wireless communication antennas are mounted on vehicles. In the case of a typical broadcasting antenna for a vehicle which operates at an FM/AM broadcasting frequency band, use is made of a monopole, type of retractable antenna whose length is adjusted to an operating frequency by a motor and which is mainly installed on the outside of the vehicle. However, this retractable antenna not only causes damage to an appearance of the vehicle, but also increases noise due to air resistance while traveling.
Further, to overcome these problems, a glass antenna, which is mainly installed around a defroster of a vehicle rear window, has an advantage in that it provides a smart appearance to the vehicle and no noise while traveling, but it has a disadvantage in that the manufacturing cost of the vehicle increases due to a royalty. The glass antenna operates like a slot antenna due to a fixed size of the rear window. As such, in the case of a vehicle whose rear window has a size that is unfit for resonance of a broadcasting frequency band, a helical micro-antenna having a length of 200 mm is used as the broadcasting antenna in place of the glass antenna.
However, this micro-antenna is installed outside the vehicle, causes damage to an appearance of the vehicle, and generates noise such as wind noise while traveling due to a protruding height, like the retractable antenna. To overcome these problems, the length of the micro-antenna may be reduced. In this case, radiation efficiency is reduced.
For this reason, attention has recently been paid to a shark fin antenna apparatus for a vehicle capable of providing a good design in appearance, avoiding an increase in manufacturing cost due to a royalty, and mounting a plurality of antennas at the same time. Furthermore, attention has also been paid to an attempt to mount the broadcasting antenna in the shark fin antenna apparatus.
However, when the broadcasting antenna is mounted in the shark fin antenna apparatus, a disc having a ground plane of a 1 meter size is used. In this case, due to a restricted space in which a height of the antenna should be within 70 mm, the broadcasting antenna is formed as a small electrical antenna whose size is smaller than λ/16 of the operating frequency. This small electrical antenna has a problem in that, as its size is reduced, its radiation efficiency is sharply reduced. As such, to obtain desired radiation efficiency within the restricted space, the total physical length of an antenna radiator is increased. In this case, the operating frequency shifted to a relatively low frequency band, so that it is difficult to meet requirements of a specific frequency band, and the appearance of the vehicle is also damaged. Further, since the plurality of antennas operating at different frequency bands coexist within the restricted space, characteristics of the additionally mounted broadcasting antenna and characteristics of the previously mounted antennas are simultaneously deteriorated due to signal inference.
Thus, there is an urgent need for technology that relatively improves the radiation efficiency within the restricted space in the shark fin antenna apparatus on which the plurality of antennas and the broadcasting antenna are mounted together, prevents the signal interference, and actually provides high applicability.